[XRay] [compiler-rt] Unwriting FDR mode buffers when functions are short.

Summary:
"short" is defined as an xray flag, and buffer rewinding happens for both exits
 and tail exits.

 I've made the choice to seek backwards finding pairs of FunctionEntry, TailExit
 record pairs and erasing them if the FunctionEntry occurred before exit from the
 currently exiting function. This is a compromise so that we don't skip logging
 tail calls if the function that they call into takes longer our duration.

 This works by counting the consecutive function and function entry, tail exit
 pairs that proceed the current point in the buffer. The buffer is rewound to
 check whether these entry points happened recently enough to be erased.

 It is still possible we will omit them if they call into a child function that
 is not instrumented which calls a fast grandchild that is instrumented before
 doing other processing.

Reviewers: pelikan, dberris

Reviewed By: dberris

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D31345

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@299629 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 11 insertions, 4 deletions

diff --git a/test/xray/TestCases/Linux/fdr-mode.cc b/test/xray/TestCases/Linux/fdr-mode.cc
index 4aa3964c9..9fb54ce7b 100644
--- a/test/xray/TestCases/Linux/fdr-mode.cc
+++ b/test/xray/TestCases/Linux/fdr-mode.cc
@@ -1,7 +1,10 @@
 // RUN: %clangxx_xray -g -std=c++11 %s -o %t
-// RUN: XRAY_OPTIONS="patch_premain=false xray_naive_log=false xray_logfile_base=fdr-logging-test- xray_fdr_log=true verbosity=1" %run %t 2>&1 | FileCheck %s
-// RUN: %llvm_xray convert --symbolize --output-format=yaml -instr_map=%t "`ls fdr-logging-test-* | head -1`" | FileCheck %s --check-prefix TRACE
+// RUN: XRAY_OPTIONS="patch_premain=false xray_naive_log=false xray_logfile_base=fdr-logging-test- xray_fdr_log=true verbosity=1 xray_fdr_log_func_duration_threshold_us=0" %run %t 2>&1 | FileCheck %s
+// RUN: XRAY_OPTIONS="patch_premain=false xray_naive_log=false xray_logfile_base=fdr-unwrite-test- xray_fdr_log=true verbosity=1 xray_fdr_log_func_duration_threshold_us=5000" %run %t 2>&1 | FileCheck %s
+// RUN: %llvm_xray convert --symbolize --output-format=yaml -instr_map=%t "`ls fdr-logging-test-* | head -1`" | FileCheck %s --check-prefix=TRACE
+// RUN: %llvm_xray convert --symbolize --output-format=yaml -instr_map=%t "`ls fdr-unwrite-test-* | head -1`" | FileCheck %s --check-prefix=UNWRITE
 // RUN: rm fdr-logging-test-*
+// RUN: rm fdr-unwrite-test-*
 // FIXME: Make llvm-xray work on non-x86_64 as well.
 // REQUIRES: x86_64-linux
 
@@ -61,8 +64,6 @@ int main(int argc, char *argv[]) {
   return 0;
 }
 
-
-
 // Check that we're able to see two threads, each entering and exiting fA().
 // TRACE-DAG: - { type: 0, func-id: [[FIDA:[0-9]+]], function: {{.*fA.*}}, cpu: {{.*}}, thread: [[THREAD1:[0-9]+]], kind: function-enter, tsc: {{[0-9]+}} }
 // TRACE:     - { type: 0, func-id: [[FIDA]], function: {{.*fA.*}}, cpu: {{.*}}, thread: [[THREAD1]], kind: function-exit, tsc: {{[0-9]+}} }
@@ -80,3 +81,9 @@ int main(int argc, char *argv[]) {
 // TRACE:     - { type: 0, func-id: [[FIDB]], function: {{.*fB.*}}, cpu: {{.*}}, thread: [[THREAD1]], kind: function-exit, tsc: {{[0-9]+}} }
 // TRACE-DAG: - { type: 0, func-id: [[FIDB]], function: {{.*fB.*}}, cpu: {{.*}}, thread: [[THREAD2:[0-9]+]], kind: function-enter, tsc: {{[0-9]+}} }
 // TRACE:     - { type: 0, func-id: [[FIDB]], function: {{.*fB.*}}, cpu: {{.*}}, thread: [[THREAD2]], kind: function-exit, tsc: {{[0-9]+}} }
+
+// Assert that when unwriting is enabled with a high threshold time, all the function records are erased. A CPU switch could erroneously fail this test, but
+// is unlikely given the test program.
+// UNWRITE: header
+// UNWRITE-NOT: function-enter
+// UNWRITE-NOT: function-exit